The moulds are actualy made in Ireland by a company called Prince August.
http://www.princeaugust.ie/
There is also a company in the USA that produces moulds but their name escapes me at the moment.
Making moulds for casting pewter is actually pretty easy if you have an item you want to copy.
You just buy the suitable RTV (Ready to vulcanise) silicon which can stand temperatures above what pewter gets to and make your own mould for it.
Plenty of how tos on the web about it.